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## Elementary Hydraulics

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**Dr Stephen Nash**Room: 236 - 1st Floor Email: stephen.nash@nuigalway.ie Phone: 091 493738 Elementary Hydraulics**Teaching**Clickers • generate engagement • enable active learning • feedback on learning Peer Instruction • learn from your classmates via group discussions • interactive learning • improved understanding**Using your Clickers**Connecting Clickers: 1 2 3 4 Hold down Power button for 2 sec Connect light flashes rapidly Type in two digit code you are given Tick button lights to say you are ok**Question Types**Multiple Choice: Multiple Choice: Use ‘T’, ‘F’ keys to answer Use number/ letter keys to answer • You have 30sec to answer a question and have amaximum of 5 attempts within the time limit. • Each answer entered supersedes the previous one. After the 5th attempt, additional attempts will not be registered.**Q1. Example 1**Which of the following ancient Greeks is famous for his work on buoyancy? • Euclid • Aristotle • Archimedes • Homer • Don’t know**Q2. Example 2**A glass of water contains some ice cubes. As the ice melts, the water level in the glass: • stays the same • rises • falls • I’m not sure**Q3. Mass and Weight**Q. The weight of a pair of dumbbells, each with a mass of 200kg, when weighed on Earth and on the Moon would be.... • the same on both • more on Earth than on the Moon • less on Earth than on the Moon • not sure**Q4: Pressure**Q. Two girls – one wearing stilettos, the other wearing runners. Which exerts more pressure on the ground? • stilettos • trainers • they both exert the same pressure • don’t know**Q5. Pressure**Q. You are standing and you lift one foot off the ground. The force of your body on the ground .... • increases • stays the same • decreases • don’t know**Q6. Pressure**Q. Water is poured into an empty complex container and is then left to settle. When the water has settled fully and the liquid is stationary the water levels in the three compartments will look like: • not sure**Q7. Pressure**Q. A rectangular tank, 2m long and 1m wide, contains 0.6m depth of oil with specific weight, wo, of 7850 N m-3. Calculate the gauge pressure on the bottom of the tank? • 4710 N m-2 • 4.71 N m-2 • 7850 N m-2 • none of the above**Q8. Pressure**Q. The same tank sits on two pieces of timber with dimensions 0.1m x 0.02m x 1m. Calculate the pressure at any point on the timber surfaces? • 47,100 N m-2 • 94,200 N m-2 • 235,500 N m-2 • none of the above**Q9. Pressure**Q. A sphere is fully immersed in water. The correct pressure diagram for the sphere is: • not sure**Q10. Pressure**Q. Two brick are being held underwater. Brick B is being held at a greater depth than Brick A. How does the force required to hold Brick B in place compare to that required to hold Brick A in place? Is it: • larger • the same • smaller • not sure A B**Q11. Hydrostaic Force**Q. Imagine two reservoirs of similar depth but different surface areas. Due to a larger surface area, the volume of water in reservoir A is twice that in reservoir B. Each reservoir is held back by a dam and both dams have equal dimensions. The hydrostatic force acting on Dam B would be: • twice that acting on Dam A • half that acting on Dam A • the same as that acting on Dam A • not sure**Q12. Hydrostaic Force**Q. In the same scenario, if Dam A was twice as length of Dam B then the hydrostatic force per unit width acting on Dam B would be: • twice that acting on Dam A • half that acting on Dam A • the same as that acting on Dam A • not sure**Q13. Hydrostatic Force**Q. A barrel contains three liquids of different densities. Which of the following pressure diagrams is correct for absolute pressure? • C. • D. E. Not sure = 680 kgm-3 = 800kgm-3 = 950kgm-3**Q14. Hydrostatic Force**Q. A gate is submerged in a reservoir. Choose the diagram that best represents the distribution of pressure on the gate. • Not sure**Q15. Hydrostatic Force**Q. A curved gate is submerged in a reservoir. Choose the diagram that best represents the distribution of pressure on the gate. • Not sure**Q16. Buoyancy**Q. A rock is held in position by the tensile force, T, in a wire. If the rock is partially immersed a tank of water, by how much will T change? • It will go to zero • It will reduce by a value equal to the weight of the displaced fluid • It won’t change • It will increase by a value equal to the weight of the displaced fluid • not sure T T**Q17. Buoyancy**Q. A glass of water contains some ice cubes. As the ice melts, the water level in the glass: • stays the same • rises • falls • I’m not sure**Q18. Buoyancy**Q. Two bricks are being held underwater. Brick B is being held at a greater depth than Brick A. How does the buoyancy force on Brick B compare to on Brick A? Is it: • greater than that on Brick A • the same as that on Brick A • less than that on Brick A • not sure A B**Q19: U-tube Manometer**P The U-tube manometer shown contains mercury with a relative density of 13.6. The pipe contains water of density 1000 kg/m3. Calculate the gauge pressure, P, at the centre of the pipe. • 53,366.4 N/m2 • 62,784 N/m2 • 48,461.4 N/m2 • Not sure 0.5 m 0.4 m X X**Q20: Pistons**In a hydraulic arrangement with two pistons the small piston has a radius of 5 cm and the large piston has a radius of 20 cm. If a force of 512 N is applied to the large piston, what weight is the small piston able to lift? • 16 N • 32 N • 64 N • 128 N • Not sure ? 512 N**Q21: Pressure Difference**U-tube manometers are connected to two tanks filled with air, as shown. Which of the following shows the correct fluid levels when a single manometer is connected to both tanks? • B. C. D. E. A B 20 cm 10 cm 0 A A A A A B B B B B 20 20 20 20 20 10 10 10 10 10 0 0 0 0 0**Q22: Buoyancy**What magnitude is the upward buoyancy force on a 20 tonne floating ship? A. 20 tons B. less than 20 tons C. more than 20 tons D. need to know shape of ship E. not sure**Q23: Buoyancy**A boat carrying a large boulder is floating on a lake. The boulder is thrown overboard and sinks. The water level in the lake (with respect to the shore) A. rises B. sinks C. remains the same D. not sure**Q24: Buoyancy**Two objects of the same volume are placed in water. Object A floats and Object B sinks. The greater buoyant force is on A. Object A B. Object B C. both are same D. not enough information E. not sure A B VA = VB**Q25: Buoyancy**Two objects of the same mass are placed in water. Object A floats and Object B sinks. The greater buoyant force is on A. Object A B. Object B C. both are same D. not enough information E. not sure A B MA = MB**Q26: Flow Rate**A fluid flows through a pipe with uniform cross section area. The density ρ of the fluid decreases to half its initial value as it flows through the pipe. What is the correct statement about the average velocity V? A. V2 equals 2V1 B. V2 equals ½V1 C. V2 equals V1 D. V2 equals 4V1 E. not sure flow 1 2 1 V1 2=½ 1 V2 = ?**Q27: Flow Classification**Identify the type of flow labelled A in the diagram below. A. turbulent B. laminar C. transitional D. uniform E. not sure A**Q28: Flow Classification**A fireman is fighting a fire. His fire hose is connected to the mains. How would you classify the flow of water through the pipe assuming there are no kinks in the hose pipe? A. unsteady, non-uniform flow B. steady, uniform flow C. steady, non-uniform flow D. unsteady, uniform flow E. not sure**Q29: Flow Classification**If someone were to stand on the fire hose how would you then classify the flow? A. unsteady, non-uniform flow B. steady, uniform flow C. steady, non-uniform flow D. unsteady, uniform flow E. not sure**Q30: Continuity Equation**Water is flowing through a horizontal pipe. If the cross-sectional area of the pipe halves between points 1 and 2 what will happen to the average velocity? A. It will decrease by half B. It will stay the same C. It will double D. It will decrease by a factor of 2 E. I’m not sure Q 2 1**Q31: Continuity Equation**3 Water flows into the pipe network shown through pipe 1 at a rate Q1. Water flows out through pipes 3, 4, 6, 7 and 8. If the pipes are all of the same diameter what is the discharge from pipe 7 in terms of Q1? A. one fifth of Q1 B. one seventh of Q1 C. one sixth of Q1 D. I’m not sure 4 2 1 6 5 7 8**Q32: Momentum**Q. Two carts, of masses m and 2m, are at rest. If you push first one cart for 3 s and then the other for the same length of time, exerting equal force on each, the momentum of the lighter cart is ... A. four times that of the heavier cart B. twice that of the heavier cart C. equal to that of the heavier cart D. one-half that of the heavier cart E. I’m not sure m F 2m F**Q33: Momentum**Q. A father and son are ice-skating. The son’s weight is half his father’s. Both stand at rest facing each other. If the son pushes hard on the father’s chest, what happens? A. The child moves backward with velocity v and the father remains at rest B. The father moves backward with velocity v and the child moves backward with velocity 2v C. The father moves backward with velocity v and the child remains at rest D. The child moves backward with velocity v and the father moves backward with velocity 2v E. I’m not sure**Q34: Momentum**Q. A man jumps off a diving board. In doing so the mans momentum changes by a certain amount and that of the diving board ... A. Changes by a larger amount B. Changes by the same amount C. Changes by a smaller amount D. Doesn’t change E. I’m not sure**Q35: Momentum**Q. Cart A is at rest. An identical cart B, moving to the right, collides with cart A. They stick together. After the collision, which of the following is true? A. Carts A and B are both at rest B. Carts A and B move to the right with a speed greater than cart B's original speed C. Carts A and B move to the right with speed equal to the original speed of cart B D. Carts A and B move to the right with a speed less than cart B's original speed E. I’m not sure A B B A**Q36: Control Volumes**Q. Water flows in a U-bend pipe as shown. Choose the correct statement regarding the x-direction vector quantities for the control volume: A. P1, P2 are positive; V1, V2, FX are negative B. P1, P2 are negative; V1, V2, FX are positive C. P1, P2, V1 are positive; V2, FX are negative D. P1, P2 FX are positive; V1, V2 are negative E. I’m not sure Plan view 2 Control volume 1**Q37: Pelton Wheel**• You are designing the double-cups of a pelton wheel turbine. For what exit velocity angle, θ, will the force of the jet on the wheel be greatest? A. θ = 90 B. θ = 60 C. θ = 45 D. θ = 0 E. I’m not sure V2 FR θ θ V1 V2**Q38: Energy Equation**Q. With regard to the Bernoulli equation which of the following statements is true? A. the elevation head is always equal to the sum of the kinetic and pressure heads B. the fluid pressure is directly proportional to the fluid velocity C. multiplying the kinetic head by the weight of the fluid gives the kinetic energy D. as fluid velocity decreases kinetic energy increases E. I’m not sure**Q39: Energy Conservation**Q. An ideal fluid flows a pipe of constant diameter. Assuming steady flow and no energy losses, what kind of energy conversion occurs between points A and B if for a sudden loss of elevation as shown? A. potential energy to kinetic energy B. potential energy to pressure energy C. pressure energy to kinetic energy D. kinetic energy to pressure energy E. I’m not sure A B**2.3 m**3.2 m Q40: Syphons 2 Q. For the syphon system shown, if the discharge pipe is shortened so that the discharge point, 3, is at the same datum level as point 1, which of the following statements will be true? A. V3 will decrease in proportion to the reduction in distance between 2 and 3 B. V3 will be zero C. P2 will remain the same D. V3 will increase in proportion to the reduction in distance between 2 and 3 E. I’m not sure 1 3**Q41: Flow in Pipelines**Q. A pipeline is used to take water from a reservoir to a nearby town. If, as shown, the pipe runs uphill for some of the way, which of the following statements is true? A. Water will always flow through the pipeline as the pipe exit is below the pipe entrance B. Water will always flow through the pipeline as the exit point is below the water surface of the reservoir C. Water flow through the pipeline is dependent on the difference in pipe elevation, h D. Water will never flow uphill E. I’m not sure h**Q42: Flow in Pipelines**• A pipe which discharges to the atmosphere is used to draw off water from a large reservoir. Which of the following assumptions is not true? A. PA = Patm B. VA = 0 C. VB = 0 D. PB = Patm E. I’m not sure A Z B**Q43: Flow in Pipelines**• Which of the following correctly represents the total energy line for the reservoir-pipeline system shown? A. B. C. D. E. I’m not sure